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Advice Needed re Challenging Electrical Problem

Hi, my 2001 530i has been a joy but a recent problem has me stumped. Fuse 13 (power driver's seat and steering wheel) blows instantly unless the large connector under the driver's seat is disconnected, pointing to a short circuit under the seat.

I've removed the front two seat bolts but cannot access the rear bolts without moving the seat forward. But I cannot get power to the seat without blowing Fuse 13.

My question is this: is there anywhere I can apply 12 VDC to actuate the fore/aft seat adjustment motor? None of the pins in the power seat controller on the side of the seat seem to connect directly to the motors. The wiring diagrams in the Bentley manual are unclear, and the seat memory controls in the door complicate things further.

Does anyone know the pinout of the large connector under the seat? Do those pins connect directly to the seat motors? That seems like my last hope but if anyone has any other ideas, I'm out of ideas myself and would really appreciate your input.

Re: Advice Needed re Challenging Electrical Problem

You can not operate the motors yourself. They control themselves based on "signals" from the electronics module (seat control switch) on the side of the seat.

Once you can lift the seat (and you have to remove the plastic covers off the rear of the rails) then your best approch would be to unplug the connectors to ALL the motors and use a meter to see which one of them is shorted to ground.

Fuse 13 feeds battery on the Red/Brown wire - and that bridges to ALL the motors - so they all have battery on them all the time.

Re: Advice Needed re Challenging Electrical Problem

Thanks Jim - I'm hoping that I can remove the motor first as cn90 suggested and then push the seat forward manually to remove it. Then I'll try your suggestion to test the seat motors. I appreciate your help.

Depending on how much room you have under the (m

seat now, is it possible for you to reach some of the motor connectors?
If so, start unplugging them one at a time until the fuse doesn't blow.
When you find the bad one reconnect all of the good motors and hopefully the bad motor won't be the one you need to move the seat forward.
If your concerned about blowing a bunch of fuses and you have a little electrical background do this.
Get a 12 volt light bulb (tail light, parking light, etc) and socket with wires on it. Plug the wires in place of fuse 13. The light should be glowing bright because of the short. When you unplug the bad motor the light will go out (or almost out depending on the current draw from the other components in that circuit). It will be obvious when you find the bad motor.

Can you remove seat sides?

I seem to recall that there are clips in the sides of the seat which break easily, allowing the entire switch module to move around and there's a way to create a short at the seat controls.

I can't remember if there's a way to remove those sides at all, or at least shift them, without removing the seat. Since you say the fuse blows instantly, I am not sure you're going to find that it's a motor. The motor wouldn't be activated "instantly" if there was no signal to move from the controller. On the other hand, a lot of these devices get +12, ground and "control" input and always have +12VDC applied at all times so it's possible that a motor could be responsible on its own.

I would be tempted to try removing the door sill plate (with the logo), the plastic trim which is inboard of that, unbolting the rear of the rails (which it sounds like you have access to) and see if there's any way to manipulate, move or remove the controls and cover in case the problem is there.

Short of that (bad pun), you may wish to try disconnecting the individual motors at their connectors. You may also be able to find a resource online which tells you whether the motors always have +12VDC applied to them and are even capable of blowing the fuse without being energized by the seat controller.

Re: Can you remove seat sides?

Craig,

I was able to get the outboard plastic side off with a little damage to it, but the connector and seat controller module seem to be fine. Disconnecting motors will be the next step, but based on other posts I've searched, the most likely problem is a power lead shorted to the seat frame under a cable tie. But I definitely need to get the seat out to look for that.

Re: Can you remove seat sides?

Man, you can't catch a break.

Please do keep us up to date, including a few pics when you find your problem if you can... This may be something that needs inspection as time goes by if it seems to have failed on it's own (as opposed to lowering the seat onto foreign objects wedged underneath).

Problem Solved - Advice and Explanation

Hi - I appreciate all the helpful advice from forum members and wanted to post a followup message for others who might encounter the Fuse 13 issue.

The problem was caused by a tiny short circuit in the wiring harness under the driver's seat, right under a cable tie. Most of the cable ties are attached to the seat springs, which seem to be covered in an insulating green paint. But this one was wrapped tightly to a bare metal link between two seat springs, and over the years it wore a hole through the harness cover and the insulation of the +12VDC hot wire underneath. The solution was an easy fix with electrical tape after a week of struggling to remove the seat.

Some advice for others who may encounter this problem in the future:

1. DON'T remove the seat until you check for this problem. It was completely unnecessary and a LOT of work, since there was no power to the seat motors to manipulate the seat for easier removal.

2. There are 2 Torx bolts at the front of the seat that can be removed without taking out the seat or removing all of the trim panels, track covers, etc. Once these are removed, the entire seat will tilt back easily. You'll have to thread the wire for the seat belt tensioner out of a clip to allow the seat to fully tilt and may need to disconnect the forward/back seat drive motor, but these are obvious if you are careful in tilting the seat.

3. Make sure your negative battery cable is disconnected, and then disconnect the main electrical connector from the front of the seat. (Use a slotted screwdriver to slide the cable retainer toward the driver's door and it will pop right out.) Make SURE you do not turn the key, or preferably even reconnect the battery, until you have reconnected the main cable or you will get an air bag warning light that requires a dealer reset.

4. Disconnect one of the electrical connectors from any motor and connect a multimeter between the 12 VDC supply (the red/brown wire) and the ground wire (solid brown). These wires run to all seat motors. On a memory seat you should read infinite resistance (open circuit) between these power and ground due to the motor controllers. On the passenger side (non-memory seat) this may not be true, but it will not show a 0 ohm short circuit either.

5. Now check the resistance between the 12 VDC supply and the seat frame. This is where my short circuit was located. The bare metal brackets near the front of the seat are a good place to connect the other probe to check resistance.

6. The wiring harness is tie-wrapped to the bottom of the seat in 5 or 6 places. While watching the multimeter, push & pull on the wiring harness around each tie wrap. If you can toggle the short circuit by manipulating the harness, you've found the culprit. The hole that had been worn in my insulation was so tiny that I would never have seen it without locating it first using the multimeter.

7. If this is inconclusive, you may need to cut the tie wraps in order to be certain. I cut all of them and added a few layers of electrical tape as an insulator before replacing each tie wrap. Even if this isn't the problem, it can't hurt and may save some trouble in the future.

8. If this doesn't help, the problem could be in the seat back (there's 1 wire tie to a metal bracket behind the rigid seat back), in the steering column, or even a bad motor. But checking the wiring harness is an easy first step before you dig deeper.

9. If you decide to remove the seat and need to move the seat forward and back to access the mounting screws, you can also do that with the seat tilted back. Just remove the two Torx screws holding the drive motor to the seat transmission and remove the motor, then pull out the small square drive shaft. Chuck it in the head of an electric drill and you can move the seat back and forth by driving the transmission directly. There is a LOT of gear reduction so the seat will move quite slowly, but it will move.

Although I hope to never touch my seats again, I learned a lot from the repair and certainly hope these guidelines help someone in the future. Thanks again for all of your advice.

Thanks for following up!

Thanks.....this might help with my problem

Mine is the signal wire that seems to be the problem for the tilt function on the steering wheel where I have only 2 volt instead of the required 12 volts on the signal wire, since I assume that wire will be in the same bundle as the main power wire you had the problem with.
Am going to have a serious look at these tywraps under the seats.